Occupant type and position detection system

ABSTRACT

A method and system (10) for detecting vehicle occupant type and position utilizes a single camera unit (12) positioned, for example at the driver or passenger side A-pillar, to generate image data of the front seating area of the vehicle. The present invention distinguishes between objects, forwardly or rearwardly facing child seats, and occupants, by periodically mapping the image taken of the interior of the vehicle into an image profile (104), and utilizing image profile matching with stored profile data (110) to determine the occupant or object type. The system and method of the present invention track occupant type and position in both parallel and perpendicular directions relative to a fixed structure such as the vehicle instrument panel to optimize both the efficiency and safety in controlling deployment of a occupant safety device, such as an air bag (28).

BACKGROUND OF THE INVENTION

The present invention relates generally to motor vehicle crashdiscrimination systems utilized for actuating or deploying a passengersafety restraint, and more specifically to a system and method fordetecting occupant seating conditions so as to optimize deployment of apassenger safety restraint.

Conventional vehicle crash discrimination systems typically employ atleast one mechanical, electromechanical, or electronic accelerationsensor affixed to the vehicle for sensing vehicle acceleration. Theoutput of the sensors are supplied to a discrimination circuit forcomparison to a predetermined threshold value. If the predeterminedthreshold value is exceeded, the discrimination circuit will output asignal which actuates or deploys a passenger safety restraint, such asan air bag or passive seat belt mechanism.

However, conventional mechanical or electromechanical accelerometerbased crash discrimination systems do not account for variations inpassenger/occupant conditions in determining whether to actuate thesafety restraint. More specifically, conventional accelerometer basedcrash discrimination systems are generally designed to assume nominalconditions, such as 50th percentile male, actual presence of a vehicleoccupant, and failure of an occupant to wear a seat belt. The assumptionof these crash conditions are necessary to insure proper actuation ofthe safety restraint when severe deceleration of the vehicle is detectedby the accelerometer. Such assumptions inherently cause unnecessary,undesired, or improperly-timed actuation of the safety restraint inconditions where no occupant is present, in marginal crash situationswhere a seat belt provides sufficient safety protection for theoccupant, or in situations where the occupant is improperly positionedrelative to the safety restraint such that actuation of the safetyrestraint could potentially injure the occupant.

Thus, since conventional crash discrimination systems can notaccommodate various occupant conditions which affect the desirability ofactuating the safety restraint, they have not proven to be completelysatisfactory. In response, the prior art has attempted to overcome thesedeficiencies by providing arrangements which are generally directed atdetecting occupant presence, size, or position relative to some fixedstructure in the vehicle. The following are examples of such prior artarrangements.

U.S. Pat. No. 5,413,378 to Steffens, Jr., et al disclose a system forcontrolling an occupant restraint, such as an air bag, wherein thesystem utilizes a combination of a set of ultrasonic occupant positionsensors, and various seat and occupant weight sensors, to determineoccupant weight and position relative to fixed structure with thevehicle.

U.S. Pat. No. 5,398,185 to Omura discloses a system for optimizingdeployment of passenger restraint devices which utilizes a combinationof a plurality of seat sensors, a card reader for inputting dataregarding the physical characteristics of the occupant, and twotelecameras to compute a value characteristic of each interior vehicleelement and the occupant's estimated behavior relative thereto.

U.S. Pat. No. 5,366,241 to Kithil discloses an overhead-mounted air bagdeployment system which utilizes an overhead passenger sensor array tosense position and velocity of an occupant's head so as to controldeployment of an air bag, and to detect and provide warning when theoccupant is in an unsafe seated condition.

U.S. Pat. No. 5,074,583 to Fujita et al disclose a vehicle collisiondetection system which utilizes a plurality of seat-mounted sensors todetect occupant seating condition, position, and size in order tooptimize inflation of an air bag in a vehicle collision.

In addition, commonly owned U.S. Pat. Nos. 5,446,661 and 5,490,069 eachdisclose a method and system for vehicle crash discrimination whichcontinuously detects various vehicle occupant positions for optimizing adiscrimination analysis to achieve increased efficiency and reliabilityin actuating a safety restraint.

While these arrangements may have provided an improvement in efficiencyover conventional crash discrimination systems, there still exits a needfor a crash discrimination system which can further optimize or tailorair bag deployment based on the specific type of occupant present in thevehicle. More specifically, with the increased use and availability ofair bags in motor vehicles has come the realization that deployment ofan air bag in certain crash situations, and with certain types ofoccupants, such as infants strapped into a child safety seat, has thepotential of causing more harm to the occupant than if the air bag werenot deployed.

As noted above, this problem has become particularly acute with infantsafety seats. The prior art has attempted to distinguish passengers frominfant child seats by using conventional distance measuring techniquesto detect the amount and extent of possible occupant movement, oralternatively has used weight sensing arrangements to detect the weightof any object which might be located on the vehicle seat. In eitherarrangement, threshold values are used to classify an object as either apassenger or an inanimate object.

However, simply using weight sensors or movement monitoring has notprovided the level of discrimination between occupant types or thereliability necessary to achieving effective "smart" control over airbag deployment. As a result, a need still exist for a system which canautomatically and continually determine occupant type and position in areliable and cost effective manner.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a systemand method which automatically determines the type of occupant in avehicle seat, as well as the location of that occupant within the seatrelative to fixed structure in the interior of the vehicle, such as thedashboard or steering wheel, so as to increase efficiency andreliability in actuating or deploying a safety restraint such as an airbag.

It is another object of the present invention to provide a system andmethod which is capable of detecting the presence of either a person, arearward facing infant car seat, a forward facing infant car seat, or abox or other inanimate object, so as to increase efficiency andreliability in actuating or deploying a safety restraint such as an airbag.

It is a further object of the present invention to provide a system andmethod which determines if an occupant is in an unsafe seated positionto optimize control over deployment of an occupant safety restraint suchas an air bag or other passive restraint device.

In accordance with these and other objects, the present inventionprovides a system and method which detects occupant position and typewhich utilizes a single camera unit positioned for example at the driveror passenger side A-pillar. The present invention provides a system andmethod which distinguishes between objects, forwardly or rearwardlyfacing infant seats, and adult occupants by periodically mapping animage taken of the interior of the vehicle into image profile data, andutilizing image profile matching with stored reference profile data todetermine the occupant or object type. Instantaneous distance is alsomeasured and changes in the measured distances are tracked. All of thisinformation is than used to optimize deployment control of at least onepassenger safety restraint.

Thus, in accordance with a first aspect of the present invention, asystem for determining vehicle occupant type and position relative to afixed structure within the vehicle comprises an imaging means mounted ata single location within the vehicle interior and having a predeterminedfield of view so that a front driver side seat and a front passengerside seat are both simultaneously viewable by said imaging means, butnot simultaneously in focus as described more fully hereinbelow. Theimaging means generates an output signal representative of aninstantaneous position for any object located within the field of view.The system further includes means for storing predetermined objectprofile data characteristic of a plurality of different types of objectswhen situated in either front seat of the vehicle, and a processor meansfor identifying the type of object located in the front seats of thevehicle by comparing the imaging means output signal to thepredetermined object profile data.

In accordance with a second aspect of the present invention, a methodfor determining position of an object located in a vehicle relative to afixed structure within the vehicle comprises the steps of generatingtwo-dimensional image data representative of any objects located withina front seating area of the vehicle, generating a two-dimensional rangegrid by vertically dividing the front seating area into a plurality ofindependent regions each representative of a predetermined size of thevehicle interior, wherein the fixed vehicle structure such as theinstrument panel is located proximate to one end region, and the vehiclefront seats are located proximate with the opposite end region,detecting lateral location of the object relative to a narrow depth offocus reference plane using a de-blurring filter, and determiningdistance from the fixed structure by comparing the generated image datawith the range grid to detect which if any of the plurality of regionsare occupied by an object.

In achieving both of these aspects, the system and method of the presentinvention further comprise discriminating between objects and occupants;A-pillar positioning of the imaging system; use of a perspective anglecorrection lens; use of a two-dimensional range grid; tracking thechange in instantaneous occupant position to predict a crash situation;optimization of passenger restraint deployment based on theidentification of occupant type and position; generating thetwo-dimensional range grid by either etching the grid on a lens element,printing the grid on a CCD element, or utilizing suitable programming ina processor means; and estimating occupant lateral distance from a fixedvehicle interior component by utilizing a narrow depth of focus lens incombination with suitable electromechanical or image processingauto-focus techniques.

The present invention will be more fully understood upon reading thefollowing detailed description of the preferred embodiment inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a vehicle occupant type andposition detection system in accordance with the present invention;

FIG. 2 is a side view of the vehicle interior showing location of thesystem of the present invention;

FIG. 3 is a downward view of the vehicle interior illustrating the fieldof view for the system of the present invention;

FIGS. 4 (a) and (b) are a side view of a "person" type occupant and thecorresponding two dimensional ranging grid image of the presentinvention;

FIGS. 5 (a) and (b) are a side view of an infant safety seat and thecorresponding two dimensional ranging grid image of the presentinvention; and

FIG. 6 is a flowchart illustrating the operation of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring to FIG. 1, there is shown a system 10 which determines vehicleoccupant position and type in accordance with the present invention. Inaccordance with the preferred embodiment, system 10 is suitably adaptedfor mounting in a single location, such as the driver or passenger sideA-pillar location as shown in FIG. 2, so as to have a field of viewallowing the system to "see" any region within the driver side seat andthe passenger side seat area for a given focal depth. The use of asingle location advantageously reduces the amount of necessary hardware,and therefore the cost and complexity of manufacturing and installationof the present invention.

More specifically, in accordance with the preferred embodiment, a singlecamera unit 12 is located at the A-pillar or similar location so as tohave a perspective field of view simultaneously covering both driver andpassenger side seats. The camera unit 12 is preferably a low light infrared (IR) sensitive type camera system, and is arranged to provide alllight operation through the inclusion of a supplemental light source,such as represented by an LED 14. However, one of ordinary skill in theart will readily appreciate that other types of camera systems may besuitable, and as such the use of an IR camera system 12 is not to beconstrued as limiting the present invention.

A perspective angle correcting lens 16 is employed to translate theperspective image of the interior of the vehicle into a two-dimensionalimage signal which is then output to an image processor 18. In otherwords, lens 16 is optically designed to effectively remove the"perspectiveness" of the image created by the slant angle of the camera12 with respect to a plane passing perpendicular to the instrument panelthrough the center of the passenger seat, as more clearly shown in FIG.3. The correction lens 16 removes distortion in the image pixelsinherently caused by the perspective view and makes the pixels all equalin actual distance spacing as if being two-dimensionally viewed from theside of the vehicle.

In further accordance with the present invention, system 10 utilizes ade-blurring filter arrangement 19 in conjunction with a narrow depth offocus reference plane. With a narrow depth of focus, points along aperpendicular plane are in focus, and objects either farther or closerthan this plane are out of focus. Thus, the location of an objectrelative to the focus plane can be inferred from the amount of blur inthe image, i.e., the farther an object is laterally displaced from thefocus plane, the more the image will be blurred.

The de-blurring filter, while symbolically shown in FIG. 1, ispreferably implemented as an algorithm subroutine in image processor 18.Therefore, with a narrow depth of focus and de-blurring filterarrangement, image processor 18 is able to infer or estimate thelocation of an object relative to the focus plane, while also being ableto ignore or distinguish background clutter within the viewable image,such as door features or the driver depending on which side of the carthe system is located, from the desired image of the occupant or objectwithin the seat.

The system 10 further includes a grid pattern 20 that is either etchedon the lens 16, screen printed on a CCD, or implemented by suitableprogramming within the image processor 18. This grid pattern iscustomized for each model of automobile, and as best illustrated inFIGS. 4(a)-(b) and 5(a)-(b) provides an actual distance spacing metricfor the pixels in the image along the plane perpendicular to theinstrument panel. As described hereinbelow, the grid pattern 20 is themechanism by which the image processor 18 will be able to measure theactual distance of objects within the image focal plane, and tootherwise detect dominate features of an object or occupant located inthe vehicle seat. The grid is effectively normalized by using laterallocation derived from the narrow depth of focus reference plane and thede-blurring filter arrangement.

In addition, the light source is preferably etched with a matchingpattern of grid marks. The relative warping of the transmitted light bythe occupant provides for detection of fine shape features which may notbe otherwise discernable in poor lighting conditions due to reducedimage contrast. Such a warped grid analysis also provides athree-dimensional profile of the occupant which can be used inconjunction with the detected lateral distance to provide comprehensiveinformation regarding occupant size, shape, and location within avehicle seat.

The overall operation of the present invention as well as the remainingelements of FIG. 1 will now be discussed in context with the flow chartshown in FIG. 6. At step 100, the camera unit 12 generates a perspectiveimage signal which is translated at step 102 by lens 16 into atwo-dimensional image data signal representative of the profile of anyobjects located within a front seat of the vehicle. At step 104, atwo-dimensional spacing or range grid is created by vertically dividingthe two-dimensional image of the front vehicle seating area into aplurality of independent regions each representative of a predeterminedsize of the vehicle interior. The grid is oriented so as tosubstantially locate the fixed vehicle structure at one end region, andthe vehicle front seats substantially at the opposite end region, asparticularly shown in FIGS. 4(b) and 5(b).

At step 106, the two-dimensionally generated image data is analyzedagainst the spacing grid to detect which if any of the plurality ofregions are occupied by an object or occupant. The image processor 18utilizes an image analysis algorithm which detects the dominant featuresand position of the object located in the vehicle seat at step 108.These features include the relative extent of the vertical portion ofthe occupant relative to the horizontal portion as shown in FIGS. 4(b)or 5(b).

Object profile data representative of a set of reference features ofvarious types of occupants, such as humans, forward and rearward facinginfant safety seats, or other inanimate objects, are stored in asuitable memory device 21, such as a RAM or EEPROM. The stored sets ofreference features are scaled to allow identification of a completerange of occupant sizes, i.e., small children to large adults. Inaddition, since there are a variety of different sized infant seats, asize invariant classification of reference features is provided forproper identification of infant seats. Image processor 18 thandetermines occupant type at step 112 by mapping or comparing thedetected dominant features of the two dimensional image signal with theset of reference features stored in memory 21 at step 110.

In addition to determining occupant type, the distance between theoccupant and the instrument panel or steering wheel of the vehicle isdetected at step 114 by measuring the relative location of the occupantbased on the regions of the two-dimensional grid which are detected asbeing occupied at step 106. The actual distance is derived by combiningthe measured location within the grid with the lateral location of theobject relative to narrow focus plane provided by the camera lens asdetermined by the de-blurring filter operation.

The motion of the occupant is determined by looking for areas ofrelative motion and instantaneous distance changes through the gridzones, and to estimate the relative speed of the motion in these areas.Such information and the respective instantaneous changes in distanceare stored, such as in memory 21. At step 116, the data generated fromthis process is compared with contemporaneous vehicle speed data inputon a line 22 from a centralized microprocessor air bag deploymentcontrol unit 24, or directly from one or more vehicle accelerationsensors (not shown). This comparison step facilitates an analysis byeither processor 18 or 24 of the motions of the occupants during eitherprecrash or noncrash braking situations, which subsequently allowsprocessor 24 to predict the onset of a crash and/or to develop anoptimal deployment strategy for the air bags, or other restraints suchas pretensioners and energy management systems.

After determining occupant type and position at steps 112 and 116respectively, at step 118 the image processor 18 provides an outputsignal 26 to the control unit 24, which subsequently optimizes controlover the actuation, or deployment, of one or more passenger safetyrestraints, such as an air bag 28, or the activation of an audible orvisual warning device(s) 30 via at least one output line 32. The warningdevices 30 provide an alert for the vehicle occupant of a potentiallyhazardous seating condition.

Therefore, with the present invention, the vehicle occupant type andposition detection system 10 is designed to provide both high frequencydetection of the type of occupant or object located in a vehicle, andmeasurements of the position of the driver and/or passengers relative topotential impact points such as the steering wheel and dashboard, and toprocess that information so as to provide an optimized safety restraintdeployment decision. The system 10 thus allows the deployment controlprocessor unit 24 to refrain from deploying an air bag when a infantsafety seat is present, particularly a rearward facing infant seat, orwhen a person is present but is too close, thereby preventing theexplosive force with which an air bag is inflated from doing substantialharm to the infant or person.

It will be further understood that the foregoing description of thepreferred embodiment of the present invention is for illustrativepurposes only, and that the various structural and operational featuresherein disclosed are susceptible to a number of modifications, none ofwhich departs from the spirit and scope of the present invention asdefined in the appended claims.

We claim:
 1. A system for determining vehicle occupant type and positionrelative to a fixed structure within the vehicle comprising:an imagingmeans mounted at a single location within the vehicle interior andhaving a predetermined field of view so that front driver side seat anda front passenger side seat are both simultaneously viewable by saidimaging means but not simultaneously in focus, wherein said imagingmeans generates an output signal representative of an instantaneousposition of any object located within the field of view; a narrow depthof focus lens operatively coupled to said imaging means, wherein saidnarrow depth of focus lens has an optic axis; a de-blurring filter,wherein said de-blurring filter cooperates with said narrow depth offocus lens to provide a measure of distance along said optic axis tosaid object within the field of view relative to the fixed structure ofthe vehicle; a memory for storing predetermined object profile datacharacteristic of a plurality of different types of objects whensituation in either front seat of the vehicle; and a processor meansoperatively coupled to said de-blurring filter for identifying the typeof object located in the front seats of the vehicle by comparing saidimaging means output signal to said predetermined object profile data.2. The system of claim 1 wherein said processor means comprises meansfor determining the distance between an object located within the fieldof view and the fixed structure within the vehicle based on said imagingmeans output signal.
 3. The system of claim 2 further comprising meansfor optimizing deployment of a passenger safety restraint based on theidentified type of object and distance.
 4. The system of claim 3 furthercomprising means for storing instantaneous distance measurements, andmeans for tracking changes in the instantaneous distance measurements,wherein said means for optimizing safety restraint deployment comprisesmeans for predicting a vehicle crash based on said tracked changes indistance.
 5. The system of claim 1 wherein said single locationcomprises a vehicle A-pillar, and wherein said imaging means furthercomprises a perspective angle correction lens for translating thepredetermined field of view from a perspective view to a two-dimensionalview.
 6. The system of claim 1 further comprising means for optimizingdeployment of a passenger safety restraint based on the identified typeof object.
 7. The system of claim 1 wherein said processor means isresponsive to said measure of distance along said optic axis to saidobject within the field of view relative to the fixed structure of thevehicle.
 8. A system for determining vehicle occupant type and positionrelative to a fixed structure within the vehicle comprising:an imagingmeans mounted at a single location within the vehicle interior andhaving a predetermined field of view so that a front driver side seatand a front passenger side seat are both simultaneously viewable by saidimaging means, wherein said imaging means generates an output signalrepresentative of an instantaneous position of any object located withinthe field of view; a memory for storing predetermined object profiledata characteristic of a plurality of different types of objects whensituated in either front seat of the vehicle; a processor mans foridentifying the type of object located in the front seats of the vehicleby comparing said imaging means output signal to said predeterminedobject profile data, said processor means comprising means fordetermining the distance between an object located within the field ofview and the fixed structure within the vehicle based on said imagingmeans output signal; means for generating two-dimensional image datarepresentative of any objects located within the predetermined field ofview; and means for generating a two-dimensional range grid whichvertically divides the field of view into a plurality of independentregions each representative of a predetermined size of vehicle interiorspace, wherein said grid if oriented so that the fixed vehicle structureis located proximate with one end region, and the vehicle front seatsare located proximate with the opposite end region, wherein said meansfor determining distance comprises means for comparing said generatedtwo-dimensional image data with said range grid to detect which if anyof the plurality of regions are occupied by an object.
 9. The system ofclaim 8 wherein said imaging means comprises a lens element, and saidmeans for generating a two-dimensional range grid comprises a gridpattern etched on the surface of said lens element.
 10. The system ofclaim 9 wherein said imaging means further comprises means fortransmitting light into the predetermined field of view, and said meansfor generating a two-dimensional range grid further comprises a gridpattern etched onto said light transmitting means which matches saidgrid pattern etched onto said lens element.
 11. The system of claim 8wherein said imaging means comprises a CCD element, and said means forgenerating a two-dimensional range grid comprises a grid printed on saidCCD element.
 12. The system of claim 11 wherein said imaging meansfurther comprises means for transmitting light into the predeterminedfield of view, and said means for generating a two-dimensional rangegrid further comprises a grid pattern etched onto said lighttransmitting means which matches said grid pattern et etched onto saidCCD element.
 13. The system of claim 8 further comprising a narrow depthof focus lens coupled to said imaging means and a de-blurring filtercoupled to said processor means, wherein the front driver side seat andthe front passenger side seat are not simultaneously in focus by saidimaging means, said means for determining the distance is responsive tosaid narrow depth of focus lens, said de-blurring filter, and saidtwo-dimensional grid for estimating the absolute distance based on thelateral location of the object within the field of view relative to thefixed structure of the vehicle.
 14. The system of claim 8 wherein saidmeans for generating two-dimensional image data comprises a processorhaving a deblurring algorithm.
 15. The system of claim 8 furthercomprising means for optimizing deployment of a passenger safetyrestraint based on the identified type of object and distance.
 16. Thesystem of claim 15 further comprising means for storing instantaneousdistance measurements, and means for tracking changes in theinstantaneous distance measurements, wherein said means for optimizingsafety restraint deployment comprises means for predicting a vehiclecrash based on said tracked changes in distance.
 17. The system of claim8 wherein said single location comprises a vehicle A-pillar, and whereinsaid imaging means further comprises a perspective angle correction lensfor translating the predetermined field of view from a perspective viewto a two-dimensional view.
 18. The system of claim 8 further comprisingmeans for optimizing deployment of a passenger safety restraint based onthe identified type of object.
 19. A method for determining position ofan object located in a vehicle relative to a fixed structure within thevehicle comprising the steps of:generating two-dimensional image datarepresentative of any objects located within a front seating area of thevehicle; generating a two-dimensional range grid by vertically dividingthe front seating area into a plurality of independent regions eachrepresentative of predetermined size of vehicle interior, wherein thefixed vehicle structure is located proximate with one end region, andthe vehicle front seats are located proximate with the opposite endregion; detecting lateral location of the object relative to a narrowdepth of focus reference plane using a de-blurring filter; andestimating the distance between the object and said fixed structure bycomparing said generated image data with said range grid and detectedlateral location to determine which if any of the plurality of regionsare occupied by an object.
 20. The method of claim 19 wherein said stepof generating a two-dimensional range grid comprises etching said gridonto the surface of a lens element used to generate said two-dimensionalimage data.
 21. The method of claim 19 wherein said step of generating atwo-dimensional range grid comprises the step of printing said grid on aCCD element used to generate said two-dimensional image data.
 22. Themethod of claim 19 wherein said step of generating a two-dimensionalrange grid comprises etching matching grid patterns onto each of a lighttransmitting and receiving component used to generate saidtwo-dimensional image data, and further comprising the step ofestimating a profile of any object located within the front area bydetecting warping of the transmitted light grid relative to thereceiving light grid.
 23. The method of claim 19 further comprising thesteps of:storing predetermined object profile data characteristic of aplurality of different types of objects when situated in either frontseat of the vehicle; and identifying the type of object located in thefront seats of the vehicle by comparing said two-dimensional image datato said predetermined object profile data.
 24. The method of claim 23further comprising the step of optimizing deployment of a passengersafety restraint based on the identified type of object and distance.25. The method of claim 24 further comprising the steps of storinginstantaneous distance measurements, and tracking changes in theinstantaneous distance measurements, wherein said optimizing stepcomprises the step of predicting a vehicle crash based on said trackedchanges in distance.
 26. The method of claim 19 wherein said step ofgenerating two-dimensional image data comprises the step of positioningan imaging system having a predetermined field of view at a singlelocation within the vehicle.
 27. The method of claim 26 wherein saidsingle location comprises a vehicle A-pillar, and wherein said step ofgenerating two-dimensional image data further comprises the step oftranslating the predetermined field of view from a perspective view to atwo-dimensional view.
 28. A method for determining position of an objectlocated in a vehicle relative to a fixed structure within the vehiclecomprising the steps of:generating two-dimensional image datarepresentative of any objects located within a front seating area of thevehicle; generating a two-dimensional range grid by vertically dividingthe front seating area into a plurality of independent regions eachrepresentative of predetermined size of vehicle interior, wherein thefixed vehicle structure is located proximate with one end region, andthe vehicle front seats are located proximate with the opposite endregion; and estimating the distance between the object and said fixedstructure by comparing said generated image data with said range grid todetermine which if any of the plurality of regions are occupied by anobject.